This invention relates to a rotary fluid displacement apparatus, and more particularly, to an improvement in a rotation preventing/thrust bearing device for an orbiting member fluid displacement apparatus.
There are several types of fluid apparatus which utilize an orbiting piston or fluid displacing member, such as a scroll, driven by a Scotch yoke type shaft coupled to an end surface of the piston or displacing member. One such apparatus, disclosed in U.S. Pat. No. 1,906,142 to John Ekelhof, is a rotary machine which has an annular and eccentrically movable piston adapted to act within an annular cylinder. The annular cylinder has a radial transverse wall. One end of wall the cylinder is fixedly mounted. Another wall is formed as a cover disc connected to the annular piston, and is driven by a crank shaft. Other prior art apparatus of this type is shown in U.S. Pat. Nos. 801,182 and 3,500,119. Though the present invention applies to either type of fluid apparatus, i.e., using either an annular piston or a scroll-type piston, description will be limited to a scroll type compressor. The term piston is used generically to describe a movable member of any suitable configuration within fluid displacement apparatus.
U.S. Pat. No. 801,182 (Creux) discloses a device including two scrolls each having a circular end plate and a spiroidal or involute spiral element. These scrolls are maintained angularly and radially offset so that both spiral elements interfit to make a plurality of line contacts between their spiral curved surfaces to thereby seal off and define at least one pair of fluid pockets. The relative orbital motion of the two scrolls shifts the line contacts along the spiral curved surfaces and, as a result, the volume of the fluid pockets changes. Since the volume of the fluid pockets increases or decreases dependent on the direction of the orbital motion, the scroll type fluid displacement apparatus is applicable to compress, expand or pump fluids.
Generally, in conventional scroll type fluid displacement apparatus, one scroll is fixed to a housing and the other scroll, which is the orbiting scroll, is eccentrically supported on a crank pin of a rotating shaft to cause the orbital motion. The scroll type fluid displacement apparatus also includes a rotation preventing device which prevents the rotation of the orbiting scroll to thereby maintain both scrolls in a predetermined angular relationship during operation of the apparatus.
Sealing along the line contacts of the above conventional scroll type apparatus must be maintained because the fluid pockets are defined by the line contacts between the two spiral elements and as the line contacts shift along the surface of the spiral elements, the fluid pockets change volume due to the orbital motion of the orbiting scroll. Since the orbiting scroll in such conventional scroll type apparatus is supported in a cantilever manner, an axial slant of the orbiting scroll occurs. Axial slant also occurs because the movement of the orbiting scroll is not rotary motion around the center of the orbiting scroll, but is orbiting motion caused by eccentric movement of a crank pin driven by the rotation of a drive shaft. Several problems result from the axial slant; such as, loss of sealing of the line contact, and vibration of the apparatus during operation and noise caused by physical striking of the spiral elements. One simple and direct solution to this problem is the use of a thrust bearing device for carrying the axial load. Thus, scroll type fluid displacement apparatus have been provided with rotation preventing and thrust bearing devices within their housing.
One recent attempt to improve rotation preventing and thrust bearing devices for scroll type fluid displacement apparatus is described in U.S. Pat. Nos. 4,160,629 (Hidden et al) and 4,259,043 (Hidden et al). The rotation preventing and thrust bearing devices in these U.S. patents are integral with one another. The rotation preventing/thrust bearing device described in these U.S. patents (see, e.g., FIG. 7 of Hidden et al. U.S. Pat. No. 4,259,043), comprises one set of indentations formed on the end surface of the circular plate of the orbiting scroll and a second set of indentations formed on an end surface of a fixed plate attached to the housing. A plurality of spheres are placed between facing indentations. However, the indentations are formed directly on the end surface of orbiting scroll or the fixed plate. The production of this type of mechanism is therefore very intricate.
Referring to FIGS. 1, 2 and 3, one solution to the above disadvantage will be described. FIG. 1 is a vertical sectional view of a part of a compressor and FIG. 2 is an exploded perspective view of a rotation preventing/thrust bearing device 37'. Rotation preventing/thrust bearing device 37' surrounds a boss 273' of orbiting scroll 27' and includes an orbital portion, a fixed portion and bearings, such as a plurality of balls. The fixed portion includes (1) an annular fixed race 371' having one end surface fitted against the axial end surface of annular projection 112' of front end plate 11', and (2) a fixed ring 372' fitted against the other axial end surface of fixed race 371' to extend outwardly therefrom and cover the other end surface of fixed race 371'. Fixed race 371' and ring 372' are attached to the axial end surface of annular projection 112' by pins 373'. The orbital portion also includes (1) an annular orbital race 374', which has one end surface fitted against an axial end surface of circular plate 271' and (2) an orbital ring 375' fitted against the other axial end surface of orbital race 374' to extend outwardly therefrom and cover the other axial end surface of orbital race 374'. A small clearance is maintained between the end surface of fixed ring 372' and the end surface of orbital ring 375'. Orbital race 374' and ring 375' are attached to the end surface of circular plate 271' by pins 376'.
Fixed ring 372' and orbital ring 375' each have a plurality of holes or pockets 372a' and 375a' in the axial direction, the number of holes or pockets in each ring 372', 375' being equal. Bearing elements, such as balls or spheres 377', are placed between facing generally aligned pairs of pockets 372a', 372b' of fixed and orbital rings 372', 375', with the rings 372', 375' facing one another at a predetermined clearance.
Referring to FIG. 3, the operation of the rotation preventing/thrust bearing device 37' will be described. In FIG. 3 the center of orbital ring 375' is placed at the right side and the direction of rotation of the drive shaft is clockwise as indicated by arrow A. When orbiting scroll 27' is driven by the rotation of the drive shaft, the center of orbital ring 375' orbits about a circle of radius R.sub.o (together with orbiting scroll 27'). However, a rotating force, i.e., moment, which is caused by the offset of the acting point of the reaction force of compression and the acting point of drive force, acts on orbiting scroll 27'. This reaction force tends to rotate orbiting scroll 27' in a clockwise direction about the center of orbital ring 375'. But, as shown in FIG. 3, eighteen balls 377' are placed between the corresponding pockets 372a' and 375a' of rings 372' and 375'. In the position shown in FIG. 3, the interaction between the nine balls 377' at the top of the rotation preventing/thrust bearing device and the edges of the pockets 372a' and 375a' prevents the rotation of orbiting scroll 27'. The magnitude of the rotation preventing forces are shown as fc.sub.1 -fc.sub.5 in FIG. 3.
In the construction, as described above, the rotation preventing/thrust bearing device 37' is made up of a pair of races and a pair of rings, with each race and ring formed separately. Therefore, the parts of the rotation preventing/thrust bearing device are easy to construct and the most suitable material for each part can be selected. However, each ring is attached by pins. The rotation preventing force of the rings is thus transmitted to the attachment pins. Since the location at which the rotation preventing force of the rings act on the respective attachment pins is spaced from the location at which the pins are attached to the orbiting scroll or housing, a moment is generated which acts on the pins. If both an associated ring and race are attached by a respective pin, this spacing increases, with the result that the stress on the pin also is increased. Also, stress is placed on the attachment pins by the impact load which occurs when the compressor unit is driven at high speed. Because of these factors, it is desirable to reduce the stress in the attachment pins.